The present invention is related to a remote control apparatus which comprises a transmitter and a receiver, and more particularly to a coding system for the transmitter and receiver.
Remote control apparatus are widely used in television receivers, garage doors, security systems and other appliances and devices. Initially, a different carrier frequency was utilized for each pair of transmitters and receivers so as to isolate them from other units. In addition, various coding schemes have been utilized to encode data into digital form. A number of such transmitters and receivers include dip switches which control the coding for the transmitter and receiver. In such systems the codes can be changed by manually changing the positions of the dip switches to different positions and ensuring that the positions of the dip switches in the transmitter and receiver are the same.
The above remote control apparatus has an inherent drawback, being that the length of its address codes is limited to the pin number of the dip switch. For example, in the case of an eight-pin dip switch, only 256 possible combinations are available. In order to increase the possible combinations, the larger dip switch, such as a sixteen-pin dip switch, may be used. Such a method results in the increase in size and manufacturing cost, and also complicates its manufacturing process.
To avoid the use of dip switch, another type of remote control apparatus has been suggested, as disclosed in U.S. Pat. No. 4,529,980 issued to Liotine et al., the content of which is incorporated herein for reference. The apparatus comprises a multi-channel transmitter and receiver for controlling a plurality of functions and includes the feature of changing the codes in the receiver and transmitter in an automatic manner. When it is desired to change the address code, a program mode switch is closed in the receiver and the micro-computer recalls from the non-volatile memory the last stored code. Using this code as a start, it performs a random number generation algorithm and stores the newly generated code in the non-volatile memory and immediately transmits the new code through an infrared light emitting diode. The transmission format with the infrared light emitting diode at the receiver continues until the program mode switch is turned off. During the energization of the infrared light emitting diode in the receiver, the tranmitter is placed in closed proximity to the receiver so that it detects the code from the infrared light emitting diode and the new code is then stored in the memory of the transmitter which then produces a flashing ready signal to indicate to the operator that the programming cycle has been completed.
In this patent, the remote control apparatus comprises a radio frequency (RF) transmitter and an infrared receiver in the transmitter, and a RF receiver and an infrared transmitter in the receiver, and thus is bulky and expensive. Although the remote control apparatus eliminates the dip switches for code selection, it also removes the ability of manually changing the address code due to its automatic random number generating and changing method. In addition, since the receiver is utilized to teach the transmitter the new address code, the patent cannot be applied in the case a host transmitter is used to control several receivers with the same address code. For example, in certain home security automations, a control unit is coupled with a plurality of sensors and is used to control from a distance a plurality of devices, such as home appliances, lights, sirens and the like, when the sensors are activated. Or in the case of a commercially-available multi-event timer, it is set to control from a distance a plurality of devices at desired times, for example turning on the microwave oven at a certain hour, and turning on the video tape recorder at a different hour, and so forth. In both cases, all of the receivers in the controlled devices have to be set with the same address code. With the above patent, however, it is impossible to fulfill such a purpose.